08Scroll mask reveal

<main class="stage">
  <div class="mk-frame is-demo">
    <div class="mk-photo"></div>
  </div>
</main>

@use "../../../../site/static/demo-tokens" as *;

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-loop;
$easing: $ease-out;
$color: $subject-blue;

@include stage($stage-paper);

.mk-frame {
  position: relative;
  width: min(260px, 78vw);
  aspect-ratio: 8 / 5;
  border-radius: $r-card;
  overflow: hidden;
  box-shadow: $shadow-raised;
}

.mk-photo {
  position: absolute;
  inset: 0;
  background:
    radial-gradient(110px circle at 34% 32%, rgba(255, 255, 255, .55), transparent 60%),
    linear-gradient(150deg, $color, $subject-ink);
  mask-image: linear-gradient(100deg, transparent 0 38%, #000 58% 100%);
  -webkit-mask-image: linear-gradient(100deg, transparent 0 38%, #000 58% 100%);
  mask-size: 260% 100%;
  -webkit-mask-size: 260% 100%;
  // 기본(트리거 전) = 숨김. mask-size 가 260% 라 position 0% 는 그라디언트의 transparent(0~38%) 구간이 창 전체를 덮는다
  mask-position: 0 0;
  -webkit-mask-position: 0 0;
}

// 실사용: 진짜 IntersectionObserver 가 뷰포트에 들어올 때 .in 을 붙인다(위 <script>) — mask-position 이 오른쪽에서 왼쪽으로 쓸고 지나가며 부드러운 가장자리로 드러난다
.mk-photo { transition: mask-position 700ms $easing, -webkit-mask-position 700ms $easing; }
.mk-frame.in .mk-photo { mask-position: 100% 0; -webkit-mask-position: 100% 0; } // position 100% 는 black(58~100%) 구간이 창 전체를 덮어 완전히 드러난다

// 데모 루프: is-demo 는 같은 마스크 스윕을 keyframes 로 무한 재생한다(캡처용, 실제 스크롤 없이도 재현)
@keyframes mk-sweep {
  0%, 8%   { mask-position: 0 0;    -webkit-mask-position: 0 0; }
  45%, 60% { mask-position: 100% 0; -webkit-mask-position: 100% 0; }
  95%, 100% { mask-position: 0 0;   -webkit-mask-position: 0 0; }
}
.mk-frame.is-demo .mk-photo { animation: mk-sweep $duration $easing infinite; }

@media (prefers-reduced-motion: reduce) {
  .mk-frame.in .mk-photo,
  .mk-frame.is-demo .mk-photo {
    animation: none !important;
    transition: none !important;
    mask-position: 100% 0 !important;
    -webkit-mask-position: 100% 0 !important;
  }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffffff;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.mk-frame {
  position: relative;
  width: min(260px, 78vw);
  aspect-ratio: 8/5;
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.mk-photo {
  position: absolute;
  inset: 0;
  background: radial-gradient(110px circle at 34% 32%, rgba(255, 255, 255, 0.55), transparent 60%), linear-gradient(150deg, #2f6df6, #17141a);
  mask-image: linear-gradient(100deg, transparent 0 38%, #000 58% 100%);
  -webkit-mask-image: linear-gradient(100deg, transparent 0 38%, #000 58% 100%);
  mask-size: 260% 100%;
  -webkit-mask-size: 260% 100%;
  mask-position: 0 0;
  -webkit-mask-position: 0 0;
}

.mk-photo {
  transition: mask-position 700ms ease-out, -webkit-mask-position 700ms ease-out;
}

.mk-frame.in .mk-photo {
  mask-position: 100% 0;
  -webkit-mask-position: 100% 0;
}

@keyframes mk-sweep {
  0%, 8% {
    mask-position: 0 0;
    -webkit-mask-position: 0 0;
  }
  45%, 60% {
    mask-position: 100% 0;
    -webkit-mask-position: 100% 0;
  }
  95%, 100% {
    mask-position: 0 0;
    -webkit-mask-position: 0 0;
  }
}
.mk-frame.is-demo .mk-photo {
  animation: mk-sweep 2s ease-out infinite;
}

@media (prefers-reduced-motion: reduce) {
  .mk-frame.in .mk-photo,
  .mk-frame.is-demo .mk-photo {
    animation: none !important;
    transition: none !important;
    mask-position: 100% 0 !important;
    -webkit-mask-position: 100% 0 !important;
  }
}

var frame = document.querySelector('.mk-frame');
var io = new IntersectionObserver(function (entries) {
  entries.forEach(function (e) { if (e.isIntersecting) { e.target.classList.add('in'); io.unobserve(e.target); } });
}, { threshold: 0.3 });
io.observe(frame);

import { CSSProperties, useEffect, useRef, useState } from "react";
import styles from "./ScrollRevealMask.module.scss";

export interface ScrollRevealMaskProps {
  duration?: string;
  easing?: string;
  color?: string;
}

export default function ScrollRevealMask({
  duration = "700ms",
  easing = "ease-out",
  color = "#2f6df6",
}: ScrollRevealMaskProps) {
  const ref = useRef<HTMLDivElement>(null);
  const [inView, setInView] = useState(false);

  useEffect(() => {
    const el = ref.current;
    if (!el) return;
    const io = new IntersectionObserver(
      (entries) => entries.forEach((e) => e.isIntersecting && setInView(true)),
      { threshold: 0.3 }
    );
    io.observe(el);
    return () => io.disconnect();
  }, []);

  const style: CSSProperties = {
    transitionDuration: duration,
    transitionTimingFunction: easing,
    maskPosition: inView ? "100% 0" : "0 0",
    WebkitMaskPosition: inView ? "100% 0" : "0 0",
  };

  return (
    <div ref={ref} className={styles.frame}>
      <div className={styles.photo} style={{ ...style, background: `linear-gradient(150deg, ${color}, #17141a)` }} />
    </div>
  );
}